Method and tools for the production of a braking band for a brake disk

ABSTRACT

The invention relates to a method and tools for producing a braking band of a disk-brake disk by casting, in which the disk comprises at least two plates connected to one another by connecting elements forming an internal air-duct for the cooling of the braking band. With the method and the tools, a disk is produced in which at least one of the plates has, in its surface defining the air-ducts, at least one groove having a cross-section which becomes wider towards the air-duct.

BACKGROUND OF THE INVENTION

The subject of the present invention is a method and tools for theproduction of a braking band of a disk for a self-ventilated disk brake.

A known type of disk-brake disk with a self-ventilated braking bandcomprises basically a support bell for connection, for example, to avehicle wheel hub. The braking band, which cooperates with the calipersin order to exert the braking force on the vehicle, is connected to thebell by means of a connector. The braking band typically comprises atleast two parallel plates separated by connecting elements which fixthem together. The space between the plates forms an air duct. By virtueof the circulation of air between the plates, the disk is cooled, bothon the outer sides of the braking band, as for a solid disk, and also onits inner sides.

As is known, during the braking operation, the disks may be subject tovibrations which translate into annoying squeals. A known approach forpreventing this noise due to the vibrations of the brake disk consistsin the formation of grooves which are produced in the braking surfacesof the braking band by turning and extend throughout the thickness ofthe plates. If the stiffness of the brake disk is thus changed locally,its dynamic characteristics are changed so as to move the naturalfrequencies of the brake disk away from the frequencies which areexcited during braking.

However, these grooves in the braking surfaces of the braking band leadto technological and structural disadvantages which relate to theacoustic behaviour, to the production, and also to the mechanicalbehaviour of the disk, as well as to the type of pad required by apartially interrupted braking surface.

In fact, the production of a surface with a plurality of groovesproduced by turning requires considerable expenditure in terms of timeand cost.

When the aforementioned grooves which extend as far as the space betweenthe two plates are produced by machining, starting from the outersurface, sharp edges are formed in the connecting elements between theplates and may introduce dangerous notching effects which in turnconstitute stress raisers. Moreover, the connecting elements areweakened because of the inevitable removal of material from their endswhen, during the machining of the through-grooves, starting from theoutside and continuing towards the space between the plates,breakthrough takes place into the space.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to propose a castingcore for the production, by casting, of a braking band for a disk-brakedisk having structural and functional characteristics such as to permitsilent braking and to overcome the disadvantages mentioned above withreference to the prior art.

This object is achieved by a core for the production of a braking bandof a disk-brake disk, the band having at least two plates connected toone another by connecting elements, in which the space between theplates forms an internal air-duct for the cooling of the braking band,characterized in that the core is suitable for forming, in at least oneof the surfaces defining the air-ducts, at least one groove whichextends substantially around a circle concentric with the axis ofsymmetry of the disk and has a cross-section which becomes wider,towards the air-duct, for a predominant part of its depth.

A further object of the present invention is to propose a core-box forthe formation of a casting core according to the present invention.

This object is achieved by a core-box comprising at least two halfcore-boxes of partially complementary shape, the half core-boxes facingone another and being in contact with one another, defining an internalcavity of the core-box, the cavity comprising a central shell-shapedportion, a connecting portion, and a substantially annular disk-shapedportion which opens to the exterior through a substantially circularduct, the central portion being connected to the outer portion by meansof the connecting portion, characterized in that the cavity has theshape of the casting core according to Claim 1.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the invention, some possible embodimentsare described by way of non-limiting example below and are shown in theappended drawings, in which:

FIG. 1 is an axonometric view of a self-ventilated brake disk,

FIG. 2 shows the disk of FIG. 1 in radial section,

FIG. 3 a shows, in radial section, a first brake disk produced by meansof a core according to the invention,

FIG. 3 b shows the brake disk of FIG. 3 a in a partially-sectioned frontview,

FIG. 4 a shows, in radial section, a second brake disk produced by meansof a core according to the invention,

FIG. 4 b shows the brake disk of FIG. 4 a in a partially-sectioned frontview,

FIG. 5 a shows, in radial section, a third brake disk produced by meansof a core according to the invention,

FIG. 5 b shows the brake disk of FIG. 5 a in a partially-sectioned frontview,

FIG. 6 shows, in radial section, a fourth brake disk produced by meansof a core according to the invention,

FIG. 7 a shows, in radial section, a fifth brake disk produced by meansof a core according to the invention,

FIG. 7 b shows the brake disk of FIG. 7 a in a partially-sectioned frontview,

FIG. 8 a shows, in radial section, a sixth brake disk produced by meansof a core according to the invention,

FIG. 8 b shows the brake disk of FIG. 8 a in a partially-sectioned frontview,

FIG. 9 a shows, in radial section, a disk produced by means of a coreaccording to the invention, in which the grooves are open towards theouter surfaces of the plates,

FIG. 9 b shows the brake disk of FIG. 9 a in a partially-sectioned frontview,

FIG. 10 a shows, in radial section, a further brake disk produced bymeans of a core according to the invention,

FIG. 10 b shows the brake disk of FIG. 10 a in a partially-sectionedfront view,

FIGS. 11 and 12 show, in perspective views, the regions of intersectionbetween a connecting element and a groove inside a self-ventilatedbraking band produced by means of a core according to the invention,

FIG. 13 shows sections through particularly advantageous embodiments ofthe grooves inside a self-ventilated braking band, produced by means ofa core according to the invention,

FIGS. 14 a to 14 d show, schematically, the production of aself-ventilated brake disk by casting,

FIG. 15 shows, in radial section, a first embodiment of a core-boxaccording to the present invention,

FIGS. 16 a and 16 b show, in radial section and in a front view, thecasting core produced by means of the core-box of FIG. 15,

FIG. 17 shows, in radial section, a second embodiment of a core-boxaccording to the present invention,

FIGS. 18 a and 18 b show, in radial section and in front view, thecasting core produced by means of the core-box according to FIG. 17,

FIGS. 19 a and 19 b show, in radial section, a third embodiment of twocore-boxes for the production of a core composed of two cores accordingto the present invention,

FIGS. 20 a and 20 b show, in radial section and in front view, the twocores for the production of a composite core produced by the core-boxesof FIGS. 19 a and 19 b.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

With reference to FIG. 1, a disk-brake disk is generally indicated 1.The disk 1 extends about an axis of symmetry s. The axis of symmetry salso constitutes the axis of rotation of the brake disk 1. A brakingband 2 comprises at least two plates 3 and 3′ connected to one anotherby connecting elements 4. The braking band 2 is supported by the bell 5by means of a connector 6. The bell 5 is disposed in the centre of thebrake disk 1 and can be coupled to a vehicle hub by connecting means.Each braking plate 3, 3′ comprises an outer surface 9, 9′ and an innersurface 8, 8′, remote from the outer surface 9, 9′. The outer surfaces9, 9′ of the plates 3, 3′ are the friction surfaces of the brake disk.The inner surfaces 8, 8′ of the plates 3, 3′ define an air-duct 7.

According to one embodiment of the braking band produced by means of acore according to the invention, at least one of the inner surfaces 8,8′ has a groove 10, 10′ which becomes wider from the outer surface 9, 9′towards the air duct 7, as shown, for example, in FIG. 1.

In a braking band produced by means of a core according to theinvention, at least one of the grooves 10, 10′ extends substantiallyaround a circle concentric with the axis of symmetry s of the brake disk1.

According to one embodiment of the braking band produced by means of acore according to the invention, all of the grooves 10 are arranged onthe two inner surfaces 8, 8′ around a circle concentric with the axis ofsymmetry s of the brake disk 1.

With further advantage, the grooves 10, 10′ produced by means of a coreaccording to the invention extend around a circle arranged centrallyrelative to the width 16 of the braking band 2, dividing the plates 3,3′ structurally into two rings 17 and 17′ of equal radial width, as canbe seen, for example, from FIG. 4 a.

With yet further advantage, all of the grooves 10, 10′ around the circleare produced by means of a core according to the invention in a mannersuch as to be of the same length and to be spaced apart uniformly.

The operation of a brake disk 1 with the braking band produced inaccordance with the invention is described below with reference to FIG.2.

During a braking operation, the pads 14 are urged against the frictionsurfaces 9, 9′ of the braking band 2 of the brake disk 1. The frictionproduces a vibration of the disk which is translated into sound waves11. The amplitude of the vibration excited increases as the excitationfrequency approaches one of the natural frequencies of the disk andfades away as the excitation frequency moves away from the naturalfrequencies of the disk. By modifying the stiffness of the brake disk bymeans of grooves 10, 10′ which become wider towards the interior of thebraking band 2, it is possible to modify the natural frequencies of thedisk, moving them away from the frequencies which are excited during abraking operation. The vibrations, and hence the sound waves 11,produced consequently disappear. It has been found that the particularshape of the cross-section of the grooves 10, 10′, that is, the factthat they become wider towards the air-duct 7 for a predominant part oftheir depth, leads to an exceptional sound-damping effect. It has alsobeen found that this effect is further increased as the length of thegrooves 10, 10′ increases beyond a minimum length equal to five timestheir width.

FIGS. 3 a, 3 b show, for example, a brake disk produced by means of acore according to the present invention, in which the grooves 10, 10′are annular and concentric with respect to the axis of symmetry s.

With further advantage, all of the grooves produced by means of a coreaccording to the invention in at least one of the inner surfaces 8, 8′of the braking band 2 are uniformly spaced apart radially.

In a brake disk produced by means of a further core according to theinvention and shown in FIGS. 3 a and 3 b, the inner surfaces 8, 8′ ofthe plates 3, 3′ with the respective grooves 10, 10′ are arranged to bereflectively symmetrical, thus ensuring a substantially identicaldistribution of the rigid regions and of the yielding regions,respectively, in the two plates 3, 3′.

In a brake disk produced by means of a further core according to theinvention and shown in FIGS. 4 a and 4 b, the plates 3, 3′ of theself-ventilated braking band 2 are connected to one another by means ofconnecting elements 4 in the form of fins. The connecting elements 4 areoriented predominantly radially with respect to the axis of rotation sof the brake disk 1 and are spaced apart substantially uniformly. Eachplate 3, 3′ has, on its inner surface 8, 8′, an annular groove 10, 10′which extends around a circle arranged centrally relative to the width16 of the braking band 2. In the regions of intersection between thegrooves 10, 10′ and the fins 4, the grooves 10, 10′ extend beneath thefins 4. In other words, the fins 4 are not interrupted in theintersection regions. Moreover, the angles between the fins 4 and thegrooves 10, 10′ in the intersection regions are rounded.

In a braking band produced by means of a further embodiment of a coreand shown in FIGS. 5 a and 5 b, the first surface 8 defining theair-duct 7 has annular grooves 10′ which are out of alignment with theannular grooves 10′ provided in a second, facing surface 8′ defining theair-duct 7.

With further advantage, the grooves 10 and 10′ of the first surface 8and of the second surface 8′ are distributed radially at regularintervals and the grooves 10 of the first surface 8 are offset by onehalf interval relative to the grooves 10′ of the second surface 8′.

It is possible, by means of a core according to the invention, to formbetween the plates 3 and 3′ of the braking band 2 any number ofconnecting elements 4 with cross-sections of any shape for ensuring bothrigid coupling between the plates 3 and 3′ and the cooling air-flow 12within the air-duct 7. In the embodiment shown in FIGS. 5 a and 5 b, thetwo plates 3 and 3′ are connected by shaped fins 4 which define aplurality of ventilation ducts that are substantially radial relative tothe axis of rotation S.

A further embodiment of the core enables grooves 10, 10′ of differentdepths 13 and 13′ to be produced, as can be seen, for example, from FIG.6. The worn thickness of the plate 3′ at the moment at which one of thegrooves 10′ opens visibly towards the exterior is indicated 15.

In a brake disk produced by means of a further core according to theinvention, at least one of the grooves 10, 10′ is arranged to have adepth 13 equal to the minimum permissible thickness of the respectiveworn braking plate 3, 3′.

With further advantage, as can be seen from FIG. 6, it is possible toform, in addition to the grooves 10, 10′ of the above-mentioned depth 13equal to the minimum permissible thickness of the worn plate, furthergrooves with a depth 13′ greater than the depth 13, the depth 13′ beingindicative of a state of wear which requires replacement of the brakedisk 1 within a predetermined period of time.

FIGS. 7 a and 7 b show an embodiment of a disk brake produced by meansof a core according to the present invention in which the plates 3 and3′ of the braking band 2 are connected to one another by elements 4 ofsubstantially circular, oval, or rhombic cross-section. The elements 4are arranged along circles around the axis of rotation s and form asuccession of annular series. One or more annular grooves 10, 10′ aredisposed in the spaces between the series of connecting elements 4.

FIGS. 8 a and 8 b show a further disk produced by means of a coreaccording to the invention, in which the plates 3, 3′ of the brakingband 2 are connected to one another by means of substantiallyoval-sectioned elements 4. The elements 4 are arranged along circlesaround the axis of rotation s and form a succession of annular series.In the specific embodiment, all of the connecting elements of the sameannular series have identical cross-sections. The shapes of thecross-sections of the connecting elements may vary from one annularseries to another. Still with reference to FIG. 8 b, the connectingelements 4 of the inner annular series have an oval cross-section havingsmaller dimensions than the elements of the intermediate series. Theconnecting elements 4 of the intermediate annular series also have anoval cross-section, but of larger dimensions than the connectingelements of the inner and outer annular series. The connecting elements4 of the outer annular series have a substantially oval cross-sectionwhich becomes wider radially towards the outer circumference of thebraking band. Two annular grooves 10 are formed in the inner surface 8of the plate 3, in the region of the inner and outer series ofconnecting elements 4, and extend beneath these connecting elements inthe intersection regions. A third annular groove 10′ is formed in theinner surface 8′ of the plate 3′, in the region of the intermediateseries of connecting elements, and extends beneath these connectingelements in the intersection regions.

In a braking band produced by means of a further core according to theinvention, the grooves 10, 10′ extend throughout the thickness of therespective plates 3, 3′, as can be seen, for example, from FIGS. 9 a and9 b.

In FIGS. 10 a and 10 b, the plates 3, 3′ of the self-ventilated brakingband 2 are connected to one another by means of fin-shaped connectingelements 4. The connecting elements 4 are oriented substantiallyradially relative to the axis of rotation s of the brake disk 1 and arespaced apart substantially uniformly. Each plate 3, 3′ has a respectiveannular groove 10, 10′ which extends around a circle arranged centrallyrelative to the width 16 of the braking band 2. The substantiallytrapezoidal cross-sections of the grooves 10, 10′ become wider towardsthe air-duct 7 and are rounded in the regions of the outer and innersurfaces 9, 9′ and 8, 8′. The outer opening of each groove 10, 10′ isinterrupted by two protuberances which constitute an edge for cuttingfriction material projecting from the pads. In the intersection regionsbetween the grooves 10, 10′ and the fins 4, the grooves 10, 10′ extendbeneath the fins 4.

FIGS. 11 and 12 show, by way of non-limiting example, intersectionregions between the connecting elements 4 and the grooves 10 inside theventilation duct 7, formed by means of casting cores according to theinvention. The angles 18 between the grooves 10 and the connectingelements 4 in the intersection regions are advantageously rounded.

FIG. 13 shows the cross-sectional profiles of grooves 10 which areparticularly suitable for weakening the plates 3 locally in order toreduce the noisiness of the brake disk 1 during braking. The grooveshave trapezoidal shapes in cross-section, in accordance with FIGS. 13 ato 13 d. This particular shape enables the structural discontinuities tobe concentrated deliberately along the desired lines.

In a braking band produced by means of a core according to theinvention, the oblique sides of the trapezium are inclined at an angleof between 15° and 90° to the longer base. More advantageously, the corehas characteristics such as to produce a braking band in which theoblique sides are inclined at an angle of between 45° and 90° to thelonger base and, even more advantageously, the oblique sides areinclined at an angle of 85° to the longer base of the trapezium.

The preferred cross-section of the grooves 10, 10′ produced by means ofa core according to the invention is the shape of an isoscelestrapezium, as shown in FIG. 13 b.

It can also be seen from FIGS. 13 a to 13 e that the edges of thegrooves are rounded.

The grooves are produced by casting, by means of respectiveprotuberances on the surface of a casting core according to theinvention.

The production of a brake disk by casting, by means of a core 20according to the present invention and the production of the core 20 bymeans of a core-box 21 according to the invention will be describedbelow with reference to FIGS. 14 a to 14 d.

A brake disk is normally produced by casting by means of two moulds 22and 22′ (see FIG. 14 d) which define the external shape of the roughdisk. The moulds 22, 22′ are made, for example, of agglomerated mouldingsand.

For ventilated disks, in addition to the two moulds 22 and 22′, at leastone insert, that is, a negative form of the connecting elements 4between the two plates 3, 3′ of the braking band 2, is required. Theinsert, which is generally known as a core 20, is made, for example, ofsand solidified by means of a resin. One or more cores 20 may be used,according to the complexity of the shape to be cast.

The production of the moulds 22, 22′ and of the cores 20, respectively,constitute very important production steps because, since they can beused only once, it is necessary to produce the moulds 22, 22′ and thecore 20 with the smallest possible number of components, thus ensuringthat the brake disks 1 are produced at an advantageous cost.

The core 20 is produced by means of at least two half core-boxes 21′ and21″ and possibly additional inserts, the number and shape of which aredetermined in turn by the complexity of the shape of the core 20 (FIGS.14 a to 14 c). The shapes of the half core-boxes 21′, 21″ and of anyinserts must be such as to conform to the permissible tolerances foreach individual core 20 thus formed and to ensure that the flow of thecore material, for example, core sand pre-coated with resin, reacheseven the critical regions at the speed necessary to ensure the requiredcompactness.

In order to be able to form the cores 20 at a typical mass-productionrate, it is necessary to limit the number of inserts to the smallestpossible number and to produce the half core-boxes 21′ and 21″ in a formwhich best satisfies the above-mentioned requirements.

FIG. 15 shows a core-box for the production of the casting core 20 shownin FIG. 16. The core-box 21 is constituted by two half core-boxes 21′,21″ which have partially complementary shapes and are assembled so as tocreate, inside the core-box 21, a cavity 23 of the shape of the core 20of FIG. 16. An outer channel 24 defines the shape of a periphery orsupport 25 of the core and has a substantially rectangular radialsection. An intermediate portion 26 of the cavity 23 is disk-shaped anddefines the dimensions of an annular band 27 of the core 20. Theintermediate portion 26 of the cavity 23 is interrupted by a pluralityof bridge elements 28 which connect two surfaces 29, 29′ between whichthe intermediate portion 26 of the cavity 23 is defined.

In FIG. 15, the bridge elements 28 are distributed around thecircumference of the intermediate portion 26 and take the form ofdividing walls which extend substantially radially relative to the axiss of the core-box 21. A central portion 30 of the cavity 23 is formed asa shell substantially defining the profile of a central portion 31 ofthe core 20. The central portion 30 of the cavity 23 is connected to theannular disk-shaped intermediate portion 26 by means of a connectingportion 32. The upper half core-box 21′ has a central opening 33 whichenables the core material to be injected to form the core 20. At leastone of the half-boxes 21′, 21″ has a groove 34, 34′ on its inner surface29, 29′ defining the intermediate portion 26 of the cavity 23. Radialdividing walls 28 are formed by the coupling of respective steppedprojections 35, 35′ of complementary shape which are present on theinner sides 29, 29′ of both of the half core-boxes 21′, 21″. As canclearly be seen from FIG. 15, the grooves 34, 34′ extend through thedividing walls 28.

All of the regions of the cavity 23 are connected to one another, thusensuring that they are filled with the core material, for example, coresand, from a single opening 33 during the moulding of the core 20.

FIGS. 16 a and 16 b show the casting core 20 produced by the core-box 21of FIG. 15. Around its outer circumference, the core 20 has a peripheralportion known as the core bearing portion or simply the support 25. Thecore 20 also comprises a central portion 31 in the form of asubstantially cylindrical cap. The outer edge of the central portion 31is integral with the inner edge of an annular band 27. The annular band27 is interrupted by a plurality of openings 36. In FIG. 16, theopenings are slot-shaped and extend substantially radially relative tothe axis s of symmetry of the core 20. Moreover, the annular band 27 hasone or more protuberances 37, 37′ in the region of the grooves 34, 34′which are present on the surfaces 29, 29′ of the half core-boxes 21′,21″ in FIG. 15.

The production of a brake disk according to the present invention isexplained below with reference to FIGS. 14 a to 14 c.

After the two half core-boxes 21′, 21″ have been brought together toform the core-box 21, the core material is injected into the cavity 23through the injection opening 33, the half core-boxes 21′, 21″ havingbeen heated beforehand. The material completely fills the cavity 23,flowing from the innermost diameter towards the outermost diameter. Asthe coating resin is polymerized, the core sand permanently adopts theshape of the cavity 23, that is, it becomes the core 20. After the core20 has set, the core-box 21 is opened by moving the half core-boxes 21′and 21″ apart, releasing the core 20 from the cavity 23. This operationis particularly easy, in spite of the fact that the core hasprotuberances 37, 37′ for defining the shapes of the grooves 10, 10′.This is because each of the protuberances 37, 37′ has a cross-sectionwhich is tapered away from the annular band of the core whichconstitutes the ventilation duct of the brake disk. In other words, eachof the protuberances has positive draft angles which facilitate theremoval of the core from the mould.

In order to cast a rough brake disk, the core 20 is placed in thehalf-mould 22′, after which the half-mould 22 is positioned so as toform the casting mould. The core 20 is kept centred and in position bythe core bearing portion 25 which is positioned in suitable seatsprovided in the half-moulds 22 and 22′.

The cavities inside the mould thus formed define the shape of the roughbrake disk. During casting, the liquid iron or other material suitablefor forming a brake disk is poured into the cavity through a feed duct,of known type and therefore not described, and sets rapidly,transmitting its heat to the moulding sand. Controlled cooling thentakes place to prevent the formation of residual tensions in the brakedisk. The sand of the two half-moulds 22, 22′ and the core sand, whichhas become very fragile because of the high temperature to which it issubjected during the casting, is broken up and removed from the roughdisk by vibration. The brake disk is then machined in the usual manner.

An advantageous variant of the invention provides for the formation,inside the air-duct 7, by casting, of grooves 10, 10′ of a depth lessthan the thickness of the plates 3, 3′ of the rough brake disk andgreater than the thickness of the plates of the finished brake disk. Theouter layer of the plates 3, 3′ is removed during the machining of theouter surfaces 9, 9′, for example, by turning, and the grooves 10, 10′are consequently opened to the exterior.

Naturally, variants and/or additions may be provided for the embodimentsdescribed and illustrated.

For example, the bridge elements 28 present in the core-box 21 and therespective openings 36 in the annular band of the casting core may haveany shape and arrangement suitable for the production of the connectingelements 4 between the above-described plates 3 and 3′ of aself-ventilated braking band 2.

The grooves 34, 34′ present in the inner surfaces 29, 29′ of thecore-box 21 and the respective protuberances 37, 37′ on the annular band27 of the core 20 may adopt any shape and arrangement suitable for theproduction of the above-described grooves 10, 10′ inside the air-duct 7of a ventilated braking band.

In FIGS. 15 and 17, the grooves 34, 34′ in the first half core-box 21′and in the second half core-box 21″ are annular and are distributedradially at regular intervals and the grooves 34 of the first half-box21′ are offset by one half interval relative to the grooves 34′ of thesecond half box 21″. The shape and distribution of the grooves 34, 34′lead to a similar shape and distribution of the protuberances 37, 37′ onthe annular band 27 of the core, shown in FIGS. 16 a and 16 b.

The bridge elements 28 are formed by respective projections 35, 35′ ofcomplementary shape present on the surfaces 29, 29′ of the halfcore-boxes 21′, 21″. The projections have respective contact surfaces 40which, according to one embodiment, are flat, as shown in FIG. 17, orare shaped with steps, according to FIG. 15. The cross-sections of theprojections 35, 35′ are also tapered towards their ends so that the core20 can be removed from the half core-boxes 21′, 21″ after it has set.

In the intersection regions between grooves 10, 10′ and connectingelements 4 of the braking band 2, the cross-section of each groove 10,10′ is defined by a portion of the protuberance 37, 37′ which isdisposed over the openings 36 in the annular band 27 of the core. Thecross-section of this portion is in turn defined both by the inner sidesof the grooves 34, 34′ in one of the two half core-boxes and by thecontact surface 40 of the respective projection 35, 35′ projecting fromthe opposed half core-box 21′, 21″, as can clearly be seen from FIGS. 15and 17.

FIGS. 19 a and 19 b show, in radial section, the core-boxes 21 for themoulding of a casting core 20 which is composed of two individual cores20′ and 20″ and is used for the casting of a braking band 2 in which theinner surfaces 8, 8′ of the plates 3, 3′ with the respective grooves 10,10′ are substantially reflectively symmetrical, as can be seen, forexample, from FIGS. 4 a and 4 b. The use of two cores is necessary inthis case since the core 20 as a whole has a shape such as to preventits removal from the half core-boxes 21′ and 21″ after it has beenmoulded. The projections 35, 35′ in the half core-boxes 21′ and 21″,which define the shapes of the openings 36 in the annular band 27 of thecore and consequently the shapes of the connecting elements 4 betweenthe plates 3 and 3′ of the disk which, in this embodiment, are finsextending substantially radially relative to the axis of symmetry s ofthe brake disk 1, are clearly visible.

FIGS. 20 a and 20 b show the composite core 20 produced by thecore-boxes 21 of FIG. 19. The composite core 20 comprises a firsthalf-core 20′ and a second half-core 20″ in which the annular band 27′of the first half core 20′ has a shape which is substantiallyreflectively symmetrical with respect to the annular band 27″ of thesecond half-core 20″.

A braking band for a disk-brake disk produced by means of a coreaccording to the invention has many advantages.

The particular shape of the cross-sections of the grooves, that is, thefact that they become wider towards the air-duct for a predominant partof their depth, leads to an exceptional sound-damping effect.

When the grooves are of a depth less than the thickness of the platesand are completely within the braking band so that they do not affectthe braking surfaces on the outer side of the braking band, it ispossible to form the grooves precisely in the desired positions and withthe size most suitable for the purpose of advantageously modifying thedynamic characteristics of the brake disk, without affecting thefriction process between the surfaces of the disk and of the pads whichare in contact during braking.

The arrangement of the grooves in the surfaces defining the air-ductinside the braking band enables the outer surfaces to be machined easilyand avoids the machining necessary to produce the grooves, with clearsavings in terms of time and costs.

The production of the grooves by casting, by means of protuberances onthe annular band of the core, avoids the cutting of the connectingelements between the plates, which is inevitable during the productionof the grooves from the exterior. This consequently prevents both theformation of sharp edges and the weakening of the connecting elements,thus eliminating the disadvantages mentioned with reference to the priorart.

The production of the grooves in the desired shape and arrangement onthe inner surfaces defining the air-duct and remote from the outerbraking surfaces avoids both the use of special pads and the depositionof abrasive material, as occurs in the grooves of the prior art.

A braking band produced by the method and with the tools according tothe invention also provides an indication of the state of wear of thebrake disk having plates with grooves on the inner surface remote fromthe outer braking surface and of a depth such as to open visibly towardsthe outer surface at the moment when a predefined value of the wear ofthe braking plates is reached. For example, grooves with differentarrangements and depths provide an indication of the current state ofwear of the brake disk and/or of the reaching of the maximum permissiblewear of the brake disk.

A further advantage relates to the cooling of the brake disk having abraking band produced in accordance with the present invention. In factit has been seen that, as well as increasing the cooling surfaces, thegrooves in the surfaces defining the air-duct inside the braking bandalso create turbulence in the air-flow which in turn favours theexchange of heat between the plates and the air, thus achieving improvedcooling of the disk.

With grooves which extend throughout the thickness of the plate, theirparticular cross-sectional shape, which is tapered towards the frictionsurface of the braking band, prevents the deposition of abrasivematerial from the pads and favours the breaking-up of materialprojecting from the pads in the region of annular grooves. Uneven wearof the pads is consequently prevented. The production of projectionswhich can cut the material projecting from the pads even prevents theinitial formation of any projection in the region of the annular groovesrather than breaking it up, by virtue of the cross-sectional shape ofthe grooves.

The braking band 2 and the bell 5 may also be produced in two separateparts which can be coupled with one another.

Naturally, in order to satisfy contingent and specific requirements, aperson skilled in the art may apply to the method and to the tools 20,20′, 20″, 21, 21′, 21″, 22, 22′ according to the present invention forproducing a braking band 2 further modifications and variations all ofwhich, however, are included within the scope of protection of theinvention as defined by the appended claims.

1-24. (canceled)
 25. A method of producing a braking band of adisk-brake disk by casting, the band comprising at least two platesconnected to one another by connecting elements, in which the spacebetween the plates forms an internal air-duct defined by surfaces,wherein it provides for the use of a core suitable for forming, in atleast one of the surfaces defining the air-ducts, at least one groovewhich extends substantially around a circle concentric with the axis ofsymmetry of the disk and having a cross-section which becomes widertowards the air-duct for a predominant portion of its depth.
 26. Amethod of producing a braking band by casting, comprising the followingsteps: providing a core-box according to claim 24, producing a core bymeans of the core-box, producing a braking band by means of moulds andthe core, and machining and finishing the outer surfaces of the breakingband as well as the other exposed surfaces of the braking band.
 27. Amethod of producing a disk by casting, comprising the following steps:providing a core-box according to claim 24, producing a core by means ofthe core-box, producing a brake disk having a braking band by means ofmoulds and the core, machining and finishing the outer surfaces of thebraking band as well as other exposed surfaces of the brake disk.
 28. Amethod of producing a braking band by casting, comprising the followingsteps: providing a core-box according to claim 24, producing a core bymeans of the core-box, producing a braking band by means of moulds andthe core, opening grooves outwardly during the machining and finishingof the outer surfaces of the braking band, and machining and finishingthe outer exposed surfaces.
 29. A method of producing a disk by casting,comprising the following steps: providing a core-box according to claim24, producing a core by means of the core-box, producing a brake diskhaving a braking band by means of moulds and the core, opening groovesoutwardly during the machining and finishing of the outer surfaces ofthe braking band, and machining and finishing the other exposed surfacesof the brake disk.